Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling

Modeling the Atmospheric Iron Processing of Mineral Dust and Combustion Aerosols

Tuesday, December 13, 2016 - 16:00
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Mineral dust aerosols and combustion aerosols contain various types of iron that influence the carbon cycle by providing iron to HNLC regions and to regions where nitrogen fixation has a significant affect on the drawdown of atmospheric CO2. Relatively insoluble iron-containing aerosols are emitted and subsequently processed in the atmosphere, thereby acting as a source of bioavailable iron upon deposition to the ocean. We develop a simple processing mechanism in the Community Atmosphere Model version 4 (CAM4) that parameterizes acidic aerosol water processing, as well as an in-cloud parameterization of the increased dissolution rate observed for organic acid ligand complexation for several types of iron. A semi-quantitative metric is used to evaluate the model performance to the available observations; while we do not match all aspects of observations of labile iron, the model performs reasonably well in capturing the overall mean of labile iron deposition. In addition, we perform a 33-year simulation with variable meteorology, variable organic acid and sulfate emissions and include records of daily and monthly averaged combustion aerosol emissions to characterize spatial and temporal variability and trends in labile iron and fractional iron solubility from both dust and combustion aerosols. Like the spatial heterogeneity of dust variability, we observe a similar variability with total and soluble iron. We predict that the inverse relationship between total iron and fractional iron solubility is largely controlled by the presence of combustion aerosols for many ocean regions but that atmospheric processing of dust iron may be as significant in some HNLC regions. Future land-use changes that may decrease dust emissions in the future may modulate the impact of the biogeochemical feedback in some ocean regions.

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